Brush seals typically include bristles sandwiched between front and back plates. Typically, the brush seal is fixed to a machine housing via some structure and the bristles contact a rotating shaft within the machine housing to seal a high pressure area with respect to a low pressure area. Brush seals are typically used in compressors, gas and steam turbines, and pumps.
In order to accommodate shaft eccentricity which can cause leakage and bristle wear, advanced brush seals allow the brush seals to move radially with respect to a brush seal housing which is fixed to the machine housing.
Still, many machines were designed with carbon ring seals instead of brush seals. In such a machine, replacing a carbon ring seal with a brush seal requires modification of the machine housing and/or additional brush seal structure in order to fix the brush seal to the machine housing.
U.S. Pat. No. 5,351,971, for example, discloses a brush seal with bristles sandwiched between a squeeze plate and a side plate. The brush seal back plate is free to move radially with respect to the squeeze plate to accommodate shaft eccentricity. This subassembly is housed in a retaining washer fixed to the machine housing. A low friction coating is applied to the inside diameter of the back plate to reduce friction between the back plate and the rotating shaft should they come into contact. Should the shaft move in the radial direction, only the back plate will move. The sealing surface at the bristle inside diameter will not move to center itself with respect to the shaft. Also, such a brush seal cannot be easily installed in a machine housing designed to accommodate a ring seal without modifying the machine housing.
U.S. Pat. No. 5,474,305 discloses a brush seal with bristles sandwiched between front and back plates disposed in a housing bolted to the machine housing. A wave spring between the brush seal and its housing urges the brush seal bristles towards the rotating shaft and centers the brush seal about the shaft. In this design, the brush seal back plate may include a rubbing surface in case the back plate contacts the rotating shaft. Such a brush seal, however, cannot be installed in a machine housing designed to accommodate a ring seal without modifying the machine housing. Also, the wave spring assembly can be fairly complex. Both of the above patents are hereby incorporated herein by this reference.